Disturbed sleep doesn't cause Alzheimer's disease, but some sleep patterns may be more common in people who have a high genetic risk for it, a new study reports.
Those patterns include being a morning person, having shorter sleep duration and being less likely to have insomnia, according to findings published in the Aug. 19 online issue of the journal Neurology.
"We know that people with Alzheimer's disease often report depression and various sleep problems, like insomnia," said study author Dr. Abbas Dehghan, of the faculty of medicine at Imperial College London in the U.K. "We wanted to find out if there are causal relationships between different sleep patterns and depression and Alzheimer's."
His team analyzed a number of genetic studies. One compared nearly 22,000 people with Alzheimer's to nearly 42,000 others. Another compared more than 9,200 people with major depression to more than 9,500 without it. Another assessed sleep-related characteristics of more than 446,000 people.
Alzheimer's risk was determined based on genetic studies where the disease was diagnosed by autopsy or clinical examination.
Researchers found no evidence that sleep-related characteristics caused Alzheimer's. They also found no evidence of cause and effect between major depression and Alzheimer's.
The study did find some small associations between sleep habits and Alzheimer's. Specifically, people with twice the genetic risk for Alzheimer's were 1% more likely than others to be morning people, and people with twice the genetic risk of Alzheimer's had a 1% lower risk of insomnia.
Researchers emphasized that these associations are small and do not prove cause and effect.
They also noted that most of the people in the study were of European ancestry, so the results may not apply to other racial/ethnic groups.
The U.S. National Institute on Aging has more about Alzheimer's disease.